1. Field of the Invention
This invention relates to a method for producing light-scattering structures on flat optical waveguides, into which light can be coupled for making the light-scattering structures visible, wherein the light-scattering structures are applied to a surface of the optical waveguide in accordance with a predetermined arrangement prescription.
2. Discussion of Related Art
It is known to employ “free-floating” letters and representations for advertising purposes or as indicating signs. Such light-scattering structures permit individual designer solutions for illuminated monochromatic or colored indicating means.
It is known to engrave or etch symbols or letters into plates made of glass or transparent plastic. Such structures can also be applied in the plate interior with laser techniques. The structures become visible, or are excited to glow, by illuminating the plates by coupling light in via the plate edges. Customarily incandescent lights, fluorescent tubes, cold-cathode tubes (CCFL), fiber optical waveguides, light-emitting diode arrangements (LEDs), organic light-emitting diodes (OLEDs) or devices generating electro-luminescence (EL) are used for coupling in the light.
The screen-printing process is used in large numbers, particularly for back-lighting liquid-crystal indicators and LCD screens, for example. In such screens which, for example, are used in connection with portable computers or laptops, light is coupled from the side into a flat optical waveguide and is coupled out in the direction toward the indicator at scattering centers attached to the back. In this case the distribution of the scattering centers is selected so that as uniform as possible a light distribution is generated. Fewer scattering centers are arranged in that edge area of the indicator in which the light is coupled, while the density of the scattering centers is increased toward the center of the screen or of the optical waveguide. For achieving uniform coupling-out of the light, the structures applied are very complex and can only be produced by “standard methods”, such as by screen-printing. The scattering centers are moreover arranged in a grid system of points. So that this structure does not appear to the viewer in the form of individual points of light, in accordance with the prior art a diffuser, which is in the form of a scattering disk made of plastic, is arranged between the optical waveguide and the LCD indicator.
The known etching and lithographic methods are highly cost-intensive, particularly when structuring large surfaces, because it is necessary to use expensive photosensitive resists in large coating and exposure installations. Such methods are also very time-consuming, because they are subject to long processing times.
When producing identical light-scattering structures in large numbers, the use of printing and foil methods can be useful from a cost viewpoint. However, the production of individual masks or punching tools by elaborate pre-preparation is only practical in connection with large numbers of pieces. With complex structurizing patterns in particular which, for example, have fine lines or free separate structures, such as the interiors of closed rings, the manufacture of the tools is very critical in its handling, particularly with foil transfer to the surface of the components. Here the achievable minimum resolution and the “dynamics” during simultaneous printing are much wider and greatly limited during simultaneous printing of very wide and very fine structures. Also, a desired local variation of the compactness of the scattered light by different light-scattering structures or grid structures is difficult to realize.
Laser-supported methods for creating light-scattering structures, such as known interior etching by laser, wherein a structure is formed in the interior of a glass plate by lasers, are also expensive and have time-consuming applications.
In general, with methods known in the prior art it is only possible with a large outlay, if at all, to produce multi-colored and/or intensity-staggered representations or gray tints such as required with images or photographs, for example.